Pyroglutamic Acid

Pyroglutamic acid, also known as 5-oxoproline, is a derivative of the amino acid glutamine and plays a critical role in the gamma-glutamyl cycle, which is essential for glutathione production and recycling. 

This compound serves as a marker for glutathione turnover, indicating the balance of sulfur amino acid metabolism. 

Elevated levels of pyroglutamic acid can signal difficulties in maintaining adequate glutathione levels, often influenced by diet, oxidative stress, and detoxification demands. 

Under normal conditions, the gamma-glutamyl cycle efficiently recycles glutathione without accumulating metabolic byproducts. However, deficiencies in glutathione synthetase (GS) can lead to the buildup of pyroglutamic acid, causing severe metabolic concerns such as acidosis, hemolytic anemia, and central nervous system damage. 

Pyroglutamic acidosis, characterized by a high anion gap metabolic acidosis, is relatively rare and typically associated with severe disease, genetic mutations, prolonged medication use, malnutrition, renal failure, infections, or pregnancy. 

In diabetes, chronic hyperglycemia increases oxidative stress, which can elevate pyroglutamic acid levels, indicating impaired glutathione turnover. Testing for pyroglutamic acid is commonly done through urine samples to diagnose metabolic disorders and assess metabolic function.

Elevated levels may respond well to nutritional interventions, particularly glycine repletion, highlighting the importance of monitoring this compound for oxidative stress-related conditions.

What is Pyroglutamic Acid?

Pyroglutamic acid, also known as 5-oxoproline, is a derivative of the amino acid glutamine. [7., 11.]

It is naturally produced in the gamma-glutamyl cycle during glutathione production and recycling. [7.] 

Pyroglutamic acid is a marker for glutathione turnover, reflecting the balance of sulfur amino acid metabolism.

Elevated pyroglutamic acid indicates difficulties in maintaining glutathione levels, influenced by factors such as diet, oxidative stress, and detoxification demands. [6.] 

Pyroglutamic Acid in the Gamma-Glutamyl Cycle [7.] 

Under normal circumstances, the gamma-glutamyl cycle recycles glutathione and metabolic byproducts do not accumulate. Typically, the gamma-glutamyl cycle operates along the following pathway: 

• Transport Out of the Cell:

• GSH is moved out of the cell.

• An enzyme called γ-glutamylpeptidase (GGT) attaches a part of GSH (the γ-glutamyl group) to another amino acid, often cystine. This creates a new compound called γ-glutamyl amino acid and cysteinylglycine.

• Transport Back into the Cell:

• The γ-glutamyl amino acid can enter the cell again.

• Inside the cell, it is broken down to release an amino acid and pyroglutamic acid.

• Conversion to Glutamate:

• 5-oxoproline is converted into glutamate, another amino acid.

• Glutamate can then be used to make more GSH.

• Breakdown of Cysteinylglycine:

• The other product, cysteinylglycine, is broken down by an enzyme called dipeptidase (DP) into cysteine and glycine, which are amino acids.

• These amino acids are also taken back into the cell and used to make more GSH.

• Production of Glutathione

• Inside the cell, glutathione synthetase (GS) catalyzes the final step of GSH synthesis.

• It combines γ-glutamylcysteine (produced in the first step of GSH synthesis by glutamate-cysteine ligase) with glycine to form GSH.

However, in the setting of glutathione synthetase (GS) deficiency, pyroglutamic acid levels can build up and cause potentially severe metabolic concerns. 

In GS deficiency the accumulated γ-glutamylcysteine is converted to pyroglutamic acid.

Accumulation of pyroglutamic acid can cause severe metabolic acidosis, hemolytic anemia, and central nervous system damage. [7.] 

Glutathione synthetase requires ATP and magnesium as cofactors. [3.] 

Accumulation of pyroglutamic acid is known as pyroglutamic acidosis. 

Conditions and Causes Associated with Increased Pyroglutamic Acid Levels

It is important to understand that true pyroglutamic acidosis is relatively rare, and often associated with severe disease and/or genetic mutations. 

Pyroglutamic acidosis is a buildup of pyroglutamic acid leading to a high anion gap metabolic acidosis. [5.] 

Causes Associated with Pyroglutamic Acidosis

Physiological settings that cause increased oxidative stress or deplete required cofactors in the glutathione production cycle will typically cause elevations in pyroglutamic acid levels.

Long-term Medication Use

Even at therapeutic doses, prolonged use of some medications including Paracetamol (acetominophen) can deplete glutathione and increase pyroglutamic acid. [5.] 

Other medications implicated in pyroglutamic acidosis include certain antibiotics and certain antiepileptic drugs. 

Malnutrition

Lack of essential nutrients exacerbates the condition. [5.] 

Renal Failure

Kidney failure impairs the clearance of pyroglutamic acid. [5.] 

Female Sex 

Women may be more susceptible. [5.] 

Infections

Sepsis and antibiotic use, especially flucloxacillin, are common triggers. [5.] 

Pregnancy

Can increase the risk due to metabolic changes. [5.] 

Pyroglutamic Acid and Mitochondrial Oxidative Stress in Diabetes [9.] 

Chronic hyperglycemia in diabetes significantly increases mitochondrial production of reactive oxygen species (ROS), leading to oxidative stress. 

Pyroglutamic acid (PGA) plays a crucial role in glutathione metabolism, an essential antioxidant in cells. Elevated urinary levels of PGA indicate impaired glutathione turnover, often resulting from insufficient glycine or sulfur amino acids, which are necessary for glutathione synthesis. 

Excess glucose in diabetes increases ROS production. This excessive ROS production damages cellular components, contributing to diabetic complications.

In response to hyperglycemia-induced oxidative stress, cells activate various adaptive mechanisms. While these adaptations aim to reduce ROS production, they also cause energy deficits and further cellular stress, exacerbating diabetic complications.

Persistent hyperglycemia maintains excessive ROS production, leading to sustained cellular damage and contributing to diabetic complications such as endothelial dysfunction and vascular damage. In this setting, elevated pyroglutamic acid levels may be seen. [9.] 

Normal Fluctuations in Urinary Pyroglutamic Acid Levels [6.] 

One study author noted that pyroglutamic acid levels in urine exhibit unique 4-week cycles in healthy adults.

Specifically, levels above 40 µg/mg creatinine tend to decrease over four weeks, while levels below 15 µg/mg increase until reaching around 40 µg/mg. [6.] 

These cycles suggest a physiological response to maintain glutathione homeostasis.

Interestingly, the cyclic pattern is more pronounced in menstruating women, likely due to estrogen-induced oxidative stress.

However, similar patterns are observed in some men, indicating other sources of metabolic stress.

Lab Testing for Pyroglutamic Acid

Test Information, Sampling Methods and Preparation

Laboratory testing for organic acids including pyroglutamic acid is typically done in urine, although it can also be tested in blood.  

Testing may be ordered to diagnose an inborn metabolic disorder, or to assess metabolic function and gastrointestinal health in a functional medicine setting.  

Urine samples may be collected in a clinical setting; they can also be collected at home.  Some labs recommend or require a first morning void sample, to provide a concentrated sample. 

Interpretation of Pyroglutamic Acid Test Results

Optimal Levels of Pyroglutamic Acid

Optimal pyroglutamic acid levels are reported by one company as 16-34 mmol/mol creatinine. [12.] 

While some fluctuation is normal, those with stable PGA levels show resilience to metabolic stress, maintaining glutathione levels effectively. [6.] 

Monitoring PGA levels could help identify individuals at risk for oxidative stress-related conditions and guide nutritional interventions to improve glutathione status. [6.] 

Clinical Significance of Elevated Pyroglutamic Acid

Elevated levels of pyroglutamic acid have been seen with nutrient deficiencies including the required amino acid precursors cysteine and glycine; elevated pyroglutamic acid responds particularly well to glycine repletion. [8., 10.]

Elevated levels may also be seen with conditions involving elevated levels of oxidative stress including diabetes mellitus, hormone imbalance, or medication use, including acetominophen toxicity. [1., 4., 5., 6., 9.] 

Pyroglutamic aciduria has also been caused by genetic mutations in homozygotes and heterozygotes. [2.] 

Clinical Significance of Decreased Levels of Pyroglutamic Acid

Low levels of pyroglutamic acid may also be due to malnutrition causing low levels of required amino acids for glutathione production.

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